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  <meta charset="UTF-8">
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  <title>Document</title>
</head>
<body>
  <script>
    try{
      console.log(a);
    }catch(err){
      console.log(err);
      console.log(111);
    }

    console.log(222);

    function fn(num){
      // num 必须是 数字 不是 报一个自定义错误
      if(typeof num !== 'number') {
        // 自定义错误
        const err = new Error('参数必须是number类型');
        console.log(err);
        throw(err);
      }
    }
    fn('aaaa')

    console.log(333);
  </script>
</body>
</html>